Known in the art is a screw conveyer apparatus for dissolving mineral ores, including sylvinite ore (cf. German Pat. No. 231,582, cl. 12 cl, published on Feb. 21, 1911).
This screw conveyer apparatus represents a trough-shaped container filled with a solution. The inside of the apparatus houses a mixing device in the form of a spiral screw mixer with the end thereof, opposite to the are charging aperture, carrying an elevator with perforated buckets.
Said apparatus operates as follows.
Crushed polydisperse ore, generally of a maximum size class of (-7) mm, is fed into the screw conveyer apparatus to contact the solvent, the solvent being fed either concurrently with or countercurrently to the ore flow. (When separating potassium chloride from sylvinite ore, the solvent is an aqueous solution saturated with sodium chloride and heated to 100.degree.-115.degree. C.).
With the screw conveyer rotating, ore particles are suspended in the solution and fall to the bottom of the apparatus, thereby making potassium chloride pass into solution.
A portion of the settled ore particles is propelled along the bottom of the apparatus by the mixer blades, while another portion is again suspended in the solution.
The undissolved portion of the ore is discharged from the apparatus by means of the elevator with perforated buckets. When dissolving sylvinite ore, the process line is normally provided with three such screw conveyer apparatuses, two of which are intended for the dissolution of sylvinite, while the third one is meant for the recuperation of heat of the undissolved portion of the ore.
However, the screw conveyor apparatus is short-lived due to the fact that salt suspensions featuring high corrosive and abrasive properties add to the wear of the mixing device and the elevator, and also of the apparatus housing proper.
Besides, there is insufficient contact between the portion of the ore lying on the bottom of the apparatus and the solution, which is conducive to reduction of the apparatus capacity.
Also known in the art is a cascade of vertical mixers for dissolving sylvinite ore, manufactured by the West-German "Lurgi" firm.
Operation of each mixer consists in the following.
Sylvinite ore crushed to (-5) mm size class is fed into the mixer concurrently with a hot initial solution. The rotation speed of each mixer in the cascade is selected so as to preclude settling of ore particles on the bottom of the apparatus.
Concurrent delivery of ore and the hot initial solution and also low capacity of each mixer necessitate a whole cascade of 6 to 12 mixers to saturate the solution with the output component. However, such a cascade entails considerable metal and power consumption.
Also known in the art is an apparatus for dissolving mineral ores (cf. U.S. Pat. No. 3,130,016, taken as a prototype.
This apparatus includes a cylindrical housing made in the form of a vertical column, a hopper mounted coaxially therewith, a liquid phase feeding device installed in the column's lower portion, a valve for removal of the solid undissolved component, and an outlet pipe for discharging the final product.
The apparatus operates as follows.
Mineral ore and the initial solution are fed into the apparatus in a counterflow direction to each other, the initial solution flowing upwardly to be saturated with the extracted component and to be subsequently withdrawn through the outlet pipe in the upper part of the apparatus.
The apparatus is provided with a trap for undissolved calcium sulphate, which is disposed below the inlet for the initial solution.
As ore in said prior art apparatus is fed downwardly, the apparatus cannot be used for the dissolution of polydisperse ores.
This is explained by the following considerations. The ore particles pointed out in the above U.S. patent being of a size class of (0.25 to 1.41) mm, an extremely low linear velocity of the upwardly flowing solution is required to keep small undissolved ore particles from being expelled from the apparatus, which conduces to reduction in the capacity of the apparatus. Besides, since the fineness of crushing of mineral ores is limited to a size class of (-5) mm and the (+5) mm class constitutes 5 to 10% at an average size of ore particles of (-2.5) mm&gt;1.4 mm, the apparatus is practically unusable for the dissolution of sylvinite and halite ores.